[NSWI004] dprintk makes my code stable

[Jura Pelc]

So have here awkward behaving of code.


I have a block of code where originally was `dprintk` for debugging and
everything was fine.
But when I tried to remove it (for the sanity of debug output) kernel
crashed. (Both with `.configure.py --debug`)
I can't see why this is happing and most importantly WHY IS THIS HAPPENING?

both `print` and `dprintk` should not apply any change.


This is a copy of the issue:
https://gitlab.mff.cuni.cz/teaching/nswi004/2020/team-please_dont/-/issues/15
related to branch
https://gitlab.mff.cuni.cz/teaching/nswi004/2020/team-please_dont/-/tree/bugfix/K-15

file: `heap.c/search_heap_size`
When running with `dprintk`, code will run smoothly and the result is
expected.
 ```c
*((int*)scanner) = 0xC0FFEE;
dprintk("Scanning: 0x%x (%x)\n", scanner, *((int*)scanner));
if(*((int*)scanner) != 0xC0FFEE)
```

``` shell
[DEBUG src/mm/heap.c:24 search_heap_size()] Scanning: 0x800fb130 (c0ffee)
[DEBUG src/mm/heap.c:24 search_heap_size()] Scanning: 0x800fc130 (c0ffee)
[DEBUG src/mm/heap.c:24 search_heap_size()] Scanning: 0x800fd130 (c0ffee)
[DEBUG src/mm/heap.c:24 search_heap_size()] Scanning: 0x800fe130 (c0ffee)
[DEBUG src/mm/heap.c:24 search_heap_size()] Scanning: 0x800ff130 (c0ffee)
[DEBUG src/mm/heap.c:24 search_heap_size()] Scanning: 0x80100130 (c0ffee)
[DEBUG src/mm/heap.c:27 search_heap_size()] NonMatch: 0x80100130 (ffffffff)
[DEBUG src/mm/heap.c:149 heap_init()] heap_begin: 0x80001130
[DEBUG src/mm/heap.c:150 heap_init()] heap_end:   0x800ff130
[DEBUG src/mm/heap.c:151 heap_init()] heap size: 1016 bytes
Hello world!
<msim> Alert: XHLT: Machine halt

Cycles: 229951
```



When running **Without** `dprintk`, code will fail during the process.
```c
*((int*)scanner) = 0xC0FFEE;
//dprintk("Scanning: 0x%x (%x)\n", scanner, *((int*)scanner));
if(*((int*)scanner) != 0xC0FFEE)
```

``` shell
<msim> Alert: XRD: Register dump
processor 0
   0                0   at                0   v0 ffffffffc0000f20   v1
      c0ffee   a0                0
  a1                0   a2                0   a3                0   t0
           0   t1                0
  t2                0   t3                0   t4                0   t5
           0   t6                0
  t7                0   s0                0   s1                0   s2
           0   s3                0
  s4                0   s5                0   s6                0   s7
           0   t8                0
  t9                0   k0             ff01   k1                0   gp
ffffffff80000000   sp ffffffff800003e8
  fp                0   ra ffffffff80000440   pc ffffffff80000180   lo
           0   hi                0
<msim> Alert: XINT: Interactive mode
[msim]
```


-- 

S pozdravem Jiří Pelc
Matematicko-fyzikální fakulta
Univerzita Karlova
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